The invention pertains to a compact document validator subassembly that illuminates documents with a constant irradiance level of light even through the distance between the light source and the documents vary from one document to another.
In the field of bill validation, for example, validators used in vending machines and the like typically utilize optical, magnetic and other sensors to obtain data from an inserted bill. In some units, a plurality of light-emitting diode (LED) light sources and phototransistor receivers are positioned on opposite sides of a bill passageway, and generate a plurality of signals corresponding to the light transmitted through the bill as a bill moves past. The signals are processed to determine certain information, such as the position of the bill in the passageway and the authenticity of the bill. The signals are typically compared to predetermined measurements stored in memory that correspond to genuine bills.
Conventional bill validation systems utilizing LED light sources also use lenses to focus the light in order to meet system performance requirements. However, some configurations do not provide sufficient light signal intensity levels to accurately validate documents. Other designs utilize high power light sources and focusing elements and are thus costly to manufacture. In addition, because the bill passageway is generally designed to be large enough to avoid bill jams, sensor measurements are sometimes adversely effected because the sensed signal varies depending upon the distance of a bill from the light source.